Fault-Tolerant Real-Time Scheduling under Execution Time Constraints

The primary backup with deallocation approach of is a strategy for the fault tolerant online scheduling of hard real time tasks In this scheme tasks are either rejected within a short time after the request or guaranteed to be executed even in case of a processor failure In this paper several heuristics for the guarantee algorithm are investigated For the rst time di erent processor selection strategies for guarantee algorithms with execution time constraints are compared In addition the concept of a decision deadline is introduced which then leads to an extension of the primary and backup checking routines The thus modi ed checking routines are shown to achieve a lower rejection ratio for tight task deadlines and constrained scheduler execution times than the modi cation making use of task slack suggested in ETH Zurich Computer Engineering and Networks Laboratory CH Zurich email naedele tik ee ethz ch